late 14c., abaishen, from Old French abaissier "diminish, make lower in value or status" (12c.), from Vulgar Latin *ad bassiare "bring lower," from ad- "to" (see ad-) + Late Latin bassus "thick, fat, low" (see base (adj.)). Form in English altered 16c. by influence of base (adj.), thus the word is an exception from the rule that Old French verbs with stem -iss- enter English as -ish. Related: Abased; abasing.